The invention relates to a method and an installation for producing a hot-rolled steel strip from continuously cast primary material in consecutive work steps, wherein the primary material is brought to hot roll temperature after solidification and is inserted into a rolling mill for rolling out into a finished strip.
A method which is known from German Offenlegungsschrift Pat. No. 32 41 745 provides that a strip-shaped cast strand be wound into a coil immediately after leaving the casting machine and passing the transverse cutting device and then, after heating to rolling temperature, uncoiled again and fed to a rolling mill for rolling out into final cross sections. A disadvantage of this known installation is that it is difficult to heat wound up coils and a very long time at a great cost in energy and operation costs is required for this.
Known strip casting installations usually use tunnel furnaces in order to bring the primary material to the desired hot rolling temperature, wherein, however, the material strands are not coiled. A substantially lower expenditure of energy is required compared to strip coiling. In multiple-strand installations, holding furnaces must be used in any event because of the resulting long transportation distances.
Bogie hearth continuous furnaces, hoisting hearth or car-bottom furnaces are primarily taken into consideration as holding furnaces; however, all of these have various disadvantages. With the use of a bogie hearth continuous furnace, it is not possible to charge and discharge coils at different times, since when discharging a bogie hearth without another bogie hearth moving up behind it, a gap occurs which is not protected from heat radiation. The charging and discharging must therefore always be effected simultaneously. In addition, the empty bogie hearths must be brought back from the discharge side to the charge side. A subsequent heating of the car, or, at any event, of the ceramic benches, is required in order to avoid black spots (so-called skid marks). During disturbances in the rolling mill train, the coils present at the coil winding station cannot be received by the furnace. There must be an additional storage furnace for storing the coils. Both doors must be opened simultaneously during the charging and discharging of a bogie hearth, which leads to higher heat losses.
A hoisting hearth furnace requires a plurality of separately driven hoisting hearth beam systems (walking-beam type systems) in order to enable a separate charging and discharging of coils. In the event of a disturbance in the rolling mill, no coils can be received by the furnace for storage. A second furnace installation is also required in this case if coils are to be stored.
A car-bottom furnace can receive one or more coils depending on the design. If the storage capacity must be the same as the ladle contents, a plurality of car-bottom furnaces are required. The disadvantage in a plurality of furnaces is that the traveling distances to the uncoilers vary and, because of this, there is no uniformity of temperature of the coils.